1. Field of the Invention
The present disclosure generally relates to image processing and, more particularly, to an image processing apparatus for correcting the color of an output image, an image processing method therefor, and a storage medium storing a program for generating image processing parameters.
2. Description of the Related Art
Calibration is performed for the purpose of preventing variation arising from various factors of an image processing apparatus, and stabilizing the reproduction characteristics including the color and gradation of an image output from the image processing apparatus. Conventionally, many techniques have been proposed for calibration as an image correction method for an image processing apparatus. Some of these techniques measure, by using a sensor, a measurement chart formed by an image processing apparatus, and perform feedback control so that the image processing apparatus is put in a desired state. The sensor for reading the measurement chart is a measuring apparatus, such as a densitometer and a spectroscopic measuring instrument.
By incorporating the measuring apparatus in a sheet conveyance path of the image processing apparatus, the measurement chart can be read without user's intervention when the sensor reads the measurement chart to measure the measurement chart. A certain technique automatically performs such calibration (Japanese Patent Application Laid-Open No. 2010-263497).
In particular, a calibration system using a spectral colorimetry sensor is capable of measuring not only monochrome, such as cyan, magenta, yellow, and black (CMYK), but also mixed-color (multicolor) represented by a combination of respective colors, thus enabling calibration with higher accuracy and generation of an International Color Consortium (ICC) profile. As used herein, “mixed-color” refers to a color produced by a plurality of toners. For example, the red, green, and blue colors are produced by using two out of the C, M, and Y colors. The gray color is produced by using the C, M, and Y colors.
In mixed-color calibration executed by using the result of measuring a measurement chart composed of mixed-color images, the color of images under measurement is formed of a combination of the C, M, Y, and K monochromatic colors. Therefore, in mixed-color calibration, the number of patch images measured on the measurement chart remarkably increases in comparison with that in conventional monochromatic calibration executed by using the result of measuring the measurement chart composed of the C, M, Y, and K monochromatic images.
For example, even if each of the C, M, Y, and K monochromatic colors is divided into only four gradations for measurement, a total of 256 combinations of patch images are required on the measurement chart used for mixed-color calibration.
Since mixed-color calibration requires measurement of a number of patch images in this way, execution of mixed-color calibration takes remarkably longer time than execution of monochromatic calibration.
Further, in many cases, an operator who operates an image processing apparatus periodically executes calibration for the purpose of preventing variation in the reproduction characteristics of an image output from the image processing apparatus. In this case, the operator periodically executes calibration even if the image processing apparatus actually does not show significant variation in the reproduction characteristics. In the case of mixed-color calibration in which a number of patch images are measured, if the operator executes calibration even if the image processing apparatus does not show significant variation in the reproduction characteristics, a large time loss will arise.
Further, there is a problem that it is difficult for the operator to immediately determine whether time-consuming mixed-color calibration is necessary.